This invention relates to a rear shock linkage system for a suspension system of a snowmobile.
Tracked vehicles such as snowmobiles have rear suspensions generally consisting of front and rear suspension arms pivotally mounted on shafts, which are rotatably connected to a slide frame. The slide frame comprises a pair of laterally spaced apart slide rails or longitudinal skids interconnected transversely on opposing lateral sides of the snowmobile. The slide rails are in sliding contact with an endless track which contacts the snow surface and drives the snowmobile. The front and rear suspension arms pivotally interconnect the chassis of the snowmobile to the slide frame.
In many current arrangements, front and rear suspension arms pivotally interconnect the chassis to the slide frame. In one typical arrangement, the rear suspension system includes a pair of shock absorbers pivotally interconnected to the chassis, extending downward to a transverse tube that is pivotally mounted relative to the slide frame by connecting parts. Also, to attach the rear shock absorber to the transverse tube, the conventional approach is to pivotally mount the shock absorber to a bracket arm that, in turn, is fixedly attached to the transverse tube. Such a system is shown in U.S. Pat. No. 5,664,649 to Thompson et al., with the above-mentioned bracket arm designated as element 90.
In the above arrangement, it is preferable to make the bracket arm as short as possible so that the shock absorber is attached at the lowest possible point to thereby provide greater suspension travel within the confines defined by the endless track. However, a short bracket arm length creates the possibility that the shock absorber will become jammed with other suspension components and/or belt during large angular displacements of the pivoting shaft, and, correspondingly, the bracket arm. Therefore, a short bracket arm length limits flexibility in the design of the suspension linkage system.
One way to alleviate the concerns over the restriction on the design options and also provide for sufficient shock absorber travel is to attach the shock absorber to an end of an additional component that permits a higher or lower pivoting point for the additional component. Such a prior art system is shown in FIG. 1. Here, shock absorber 1 is attached to a rocker arm 2, which is pivotally attached via a bolt 3 to an additional component designated as plate bracket 4. Plate bracket 4 is in turn fixed to transverse tube 5, which is fixed to the slide frame. Thus, rocker arm 2 pivots about plate bracket 4 via bolt 3. Because of the large forces experienced by the system, plate bracket 4 and rocker arm 2 require additional support. To provide such support, plate bracket 4 includes a C-shaped portion 6, which is more clearly shown in the exploded view in FIG. 2. This C-shaped portion 6 is in sliding contact with transverse portion 8 of front suspension arm 7. Thus, plate bracket 4 is supported at both ends for additional strength. As can be seen from FIG. 1, shock absorber 1 is thus attached to a low position that allows for sufficient suspension travel. Because rocker arm 2 is long and can pivot freely about pivot 3, the concerns about the restrictions in the suspension linkage system are reduced.
However, the prior art apparatus shown in FIG. 1 has three problems. First, the added components of the plate bracket 4 and support tube 5 add weight. Second, the forces involved combined with the friction between the C-shaped portion 6 and transverse portion 8 create significant wear of both the transverse portion 8 and the C-shaped portion 6. Third, because of the forces between the C-shaped portion 6 and the transverse portion 8, xe2x80x9cstictionxe2x80x9d occurs between the two components, preventing free movement of the front suspension arm and thereby reducing the overall performance of the suspension system.
It is an object of the present invention, therefore, to overcome the problems associated with the prior art noted above. In achieving this object, the present invention provides a snowmobile suspension system comprising a slide frame for engagement an endless track, a suspension arm, a bracket arm, and a rocker arm. The suspension arm has an upper portion adapted to be pivotally mounted relative to a chassis on a snowmobile and a lower portion adapted to be pivotally mounted relative to the slide frame. The bracket arm has an end fixedly connected to the lower portion of said suspension arm. The rocker arm has an upper end pivotally connected to the other end of the bracket arm and a lower end supporting a lower end of a shock absorber, the lower end of the shock absorber being pivotally attached thereto. The upper end of the shock absorber is pivotally interconnected to the chassis.